Originally posted on Medium on 05/18/17.
*Please note that we have published this information in the International Journal of Primatology here (pdf)*
If you are at all interested in wildlife, you might have heard about the newest shocking decline. According to two new studies (Gould and Sauther 2016 and LaFleur et al. 2016), ring-tailed lemurs (Lemur catta), Madagascar’s most famous creature, have faced a 95% population decline, with as few as 2,000 individuals left in the wild. I was particularly surprised. As someone who had conducted her Master’s research in Madagascar (albeit on the other end of the island, in the northeast) I knew that ring-tailed lemurs were survivors, able to thrive in less-than-great habitats. How in the world could a species that seemed so common be so close to extinction?
Well, although wild lemurs in general (and ring-tailed lemurs, specifically) face heinous pressure due to habitat destruction/degradation and hunting, don’t light a candle for the wild ring-tailed lemur just yet. Eager to understand how such a hardy species could decline so rapidly, I combed through the two studies (and a few of the studies that they used as their data sources) and found two glaring bits of information that were left out of the worrying news.
They didn’t survey a lot of areas where ring-tailed lemurs could be.
Both of the studies came to their estimates from on-the-ground surveys or past studies of 30+ sites where ring-tailed lemurs were known to be currently or recently present. However, a number of areas (particularly a few national parks and protected forests) either went unsurveyed, ring-tailed lemurs were noted as present but individuals were not counted, or only part of the population was counted. The amount of potential habitat that went partially or completely unsurveyed amounts to at least 31,000 ha (Gould and Sauther 2016).
Gould and Sauther (2016) note this lack, saying:
The lack of rigorous sampling of ring-tailed lemurs in these areas is important for a variety of reasons, not limited to the fact that there is more unsurveyed than surveyed area. Lemur populations in protected areas are often larger than those in unprotected areas and lemurs in unprotected areas tend to be hunted, making them “shy” and harder to detect using rapid assessment methods (which LaFleur et al. 2016 in particular depended on).
The methodology could be more rigorous.
While a good portion of the sites were assessed by the authors, the majority of the data from both studies comes from previous studies. I went through 27 of the studies cited and found a few discrepancies.
For example, Gould and Sauther (2016) cite Gardner et al. (2009) to say that ring-tailed lemurs are likely extirpated from one forest. However, Gardner et al. (2009) say in the discussion that:
LaFleur et al. (2016) cite Goodman (2003) and two days of on-the-ground surveys to say that ring-tailed lemurs are extinct from Kirindy Mitea de sud. Goodman (2003), however, notes:
This both implies that Goodman (2003) a) did not completely survey Kirindy Mitea de sud (only a part of it, the Forêt d’Ankoadava) and b) that despite there being a lack of ring-tailed lemurs within the surveyed area, there were areas that might have had ring-tailed lemurs. It is likely that ring-tailed lemurs could have been missed during LaFleur et al. (2016)’s two-day surveys of the area.
Gould and Sauther (2016) note that there are 118 ring-tailed lemurs in Andohahela National Park (a protected area covering 760 square kilometers), citing two studies (Raharivololona and Ranaivosoa 2000 and Rasoarimanana 2005). Both of these studies surveyed the same sites, all seven located on the very edge of the national park. Neither studies went within the core of the protected area, where it is likely that there are unknown ring-tailed lemur populations.
Meanwhile, LaFleur et al. (2016) puts the ring-tailed lemur population within Andohahela at 82 individuals, citing Moniac and Heitmann (2007). However, Moniac and Heitmann (2007) is merely an observation of two hunted lemurs within a pit located outside the western border of the national park. I was unable to determine where LaFleur et al. (2016) got the cited “82 individuals”.
The estimate of a “95% decline” comes from LaFleur et al. (2016), which compares their estimate of 2,200 individuals from 32 sites to Sussman et al. (2006)’s estimate of Madagascar’s ring-tailed population size based on forest cover.
However, Sussman et al. (2006) characterize their estimate as “preliminary”, stating that there were a number of assumptions that they made:
Thus, although it is highly likely that there was a decline in total ring-tailed lemur population since 2000, it is unlikely that the decline was as large as 95%.
So what does this all mean?
Basically, the conclusion of 2,000–2,400 ring-tailed lemurs left in the wild is perhaps better stated as: 2,000–2,400 ring-tailed lemurs remaining at 34 sites based on a relative few on-the-ground surveys, but mainly data pulled from the literature. Gould and Sauther (2006) characterize their estimate as representing “all known populations and population extirpations as of 2016.” (p. 94). Unfortunately, as is the case for much of Madagascar’s wildlife, there still remains a lot of unsurveyed area, potentially home to unknown populations.
Again, it is highly likely that there has been a decline in ring-tailed lemur populations, due to habitat loss/degradation and hunting. However, the estimates of both studies do not include unknown populations in large chunks of forest that are yet unsurveyed; thus, they are very likely heavily underestimating the number of wild ring-tailed lemurs still left in Madagascar. I agree with Gould and Sauther (2016) that rigorous sampling of these large protected forests need to be conducted in the near future, as only that will provide us with an estimate of the true number of ring-tailed lemurs left in the wild.